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        <h3>
            Journal Papers</h3>
        <a class="pdf" href="../../Content/publications/journals/stepwise_fairshare_2009.pdf">
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            Oznur Ozkasap, Mine Caglar, <b>Emrah Cem</b>, Emrah Ahi, Emre Iskender (2009), <i>Fair-Share
                Buffering for Gossip-Based Peer-to-Peer Data Dissemination </i>, Computer Networks
            Journal, Elsevier Science, 53 (13), 2259-2274.
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            <p>
                We consider buffer management in support of large-scale gossip-based peer-to-peer
                data dissemination protocols. Coupled with an efficient buffering mechanism, system-wide
                buffer usage can be optimized while providing reliability and scalability in such
                protocols. We propose a novel approach, stepwise fair-share buffering, that provides
                uniform load distribution and reduces the overall buffer usage where every peer
                has a partial view of the system. We report and discuss the comparative performance
                results with existing buffering approaches as well as random buffering which serves
                as a benchmark. We present separate evaluations of bufferer selection and gossip-based
                data dissemination. Reliability, content dissemination time, message delay, buffering
                delay, and minimum buffer requirements are considered as the key metrics investigated
                through simulations. The performance of our approach in the case of multiple senders,
                link failures with multiple bufferers, and scalability to larger networks are investigated.
                Several power-law and hierarchical overlay topologies are considered. Analytical
                bounds for reliability of dissemination are also provided.</p>
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        <a class="pdf" href="../../Content/publications/journals/FGCS_2012.pdf">
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            <b>Emrah Cem</b>, Oznur Ozkasap, <i>ProFID: Practical Frequent Item Set Discovery in
                Peer-to-Peer Networks</i>, Future Generation Computer Systems, The International
            Journal of Grid Computing and eScience Elsevier (FGCS11), (In press).
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            <p>
                We address the problem of discovering frequent items in unstructured P2P networks
                which is relevant for several distributed services such as cache management, data
                replication, query refinement, topology optimization and security. This study makes
                the following contributions to the current state of the art. First, we propose and
                develop a fully distributed Protocol for Frequent Items Discovery (ProFID) where
                the result is produced at every peer. ProFID uses gossip-based (epidemic) communication,
                a novel pairwise averaging function and system size estimation together to discover
                frequent items in an unstructured P2P network. We also propose a practical rule
                for convergence of the algorithm. In contrast to the previous works, each peer gives
                local decision for convergence based on the change of updated local state. We developed
                a model of ProFID in PeerSim and performed various experiments to compare and evaluate
                its efficiency, scalability, applicability. The protocol’s resilience under realistic
                churn models was studied. For evaluating the effect of network dynamics, we deployed
                our protocol on the Internet-scale real network PlanetLab. We also compared the
                accuracy and scalability of ProFID with adaptive Push-Sum algorithm. Our results
                confirm the practical nature, ease of deployment and efficiency of our approach,
                and also show that it outperforms adaptive Push-sum in terms of accuracy, convergence
                speed and message overhead.</p>
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        <h3>
            Conference Papers</h3>
        <a class="pdf" href="../../Content/publications/conference/2011_ICEAEC.pdf">
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            <b>Emrah Cem</b>, Tugba Koc, Oznur Ozkasap, <i>Energy Efficient Hierarchical Epidemics
                in Peer-to-Peer Systems</i>, International Conference on Energy Aware Computing
            (ICEAC), Istanbul/Turkey, Nov 2011.
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            <p>
                Epidemic or gossip-based mechanisms are preferred in several distributed protocols
                for their ease of deployment, simplicity, robustness against failures, load-balancing
                and limited resource usage. In flat neighborhood epidemics, peers have similar responsibilities
                and all participate in gossiping via neighboring peers. We have proposed an energy
                cost model for a generic peer using flat neighborhood epidemics, and examined the
                effect of protocol parameters to characterize energy consumption. Although it has
                been shown that a peers power consumption amount is independent of population size,
                peers always need to be active to process incoming gossip messages. In this study,
                we consider power awareness features of flat and hierarchical epidemics in peer-to-peer
                (P2P) systems, and propose a power-aware hierarchical epidemic approach with its
                energy cost model and analysis. In this adaptive approach, only a subset of peer
                population is active in gossiping by forming an overlay, so that the other peers
                can switch to idle state. It also allows data aggregation that can be utilized to
                reduce gossip message size. As a case study for epidemic protocol, we use our approach
                and simulation model for frequent item set discovery in unstructured P2P networks.
            </p>
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        <a class="pdf" href="../../Content/publications/conference/2011_ISCIS.pdf">
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            <b>Emrah Cem</b>, Ender Demirkaya, Ertem Esiner, Burak Ozaydin, Oznur Ozkasap, <i>Energy
                Cost Model for Frequent Item Discovery in P2P Networks</i>, Proc. of ISCIS,
            London/UK, pp. 117-123, September 2011.
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            <p>
                For large scale distributed systems, designing energy efficient protocols and services
                has become as significant as considering conventional performance criteria like
                scalability, reliability, fault-tolerance and security. We consider frequent item
                set discovery problem in this context. Although it has attracted attention due to
                its extensive applicability in diverse areas, there is no prior work on energy cost
                model for such distributed protocols. In this paper, we develop an energy cost model
                for frequent item set discovery in unstructured P2P networks. To the best of our
                knowledge, this is the first study that proposes an energy cost model for a generic
                peer using gossip-based communication. As a case study protocol, we use our gossip-based
                approach ProFID for frequent item set discovery. After developing the energy cost
                model, we examine the effect of protocol parameters on energy consumption using
                our simulation model on PeerSim and compare push–pull method of ProFID with the
                well-known push-based gossiping approach. Based on the analysis results, we reformulate
                the upper bound for the peer’s energy cost.
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        <a class="pdf" href="../../Content/publications/conference/2010_ISCIS.pdf">
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            <b>Emrah Cem</b>, Oznur Ozkasap, <i>ProFID: Practical Frequent Item Set Discovery in
                Peer-to-Peer Networks</i>, Proc. of ISCIS, London/UK, pp. 199-202, September
            2010.
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            <p>
                This study addresses the problem of discovering frequent items in unstructured P2P
                networks. We propose a fully distributed Protocol for Frequent Item set Discovery
                (ProFID) where the result is produced at every peer. We also propose a practical
                rule for convergence of the algorithm. Finally, we evaluate the efficiency of our
                approach through an extensive simulation study on PeerSim.
            </p>
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        <h3>
            Posters & Selected Presentations</h3>
        <a class="pdf" href="../../Content/publications/posters-Presentations/2012_acm_s3_workshop.pdf">
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        <h2 class="expand">
            <b>Emrah Cem</b>, Sena Efsun Cebeci, Oznur Ozkasap, <i>A Tool for Frequent Items Discovery
                in Large-Scale P2P Networks</i>, ACM s3 Workshop, Istanbul, Turkey, August 2012.
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        <a class="pdf" href="../../Content/publications/posters-Presentations/2011_eenergy.pdf">
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            Tugba Koc,<b>Emrah Cem</b>, Oznur Ozkasap, <i>Dominating-set Based and Power-aware Hierarchical
                Epidemics in P2P Systems(Poster Presentation)</i>, 2nd International Conference
            on Energy Efficient Computing and Networking (e-Energy), New York, June 2011.
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        <a class="pdf" href="../../Content/publications/posters-Presentations/Poweraware_Hierarchical_Epidemics_Budapest.ppt">
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            <b>Emrah Cem</b>, Oznur Ozkasap, Power-Aware Hierarchical Epidemics in P2P Systems,
            COST 2nd Year Workshop, Budapest, Hungary, April 2011.
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